1. Field of the Invention
The present invention relates to a light deflecting apparatus, and more precisely, to a light scanning apparatus which scans a recording medium by reflecting a light beam incident on a reflecting surface toward an exposure surface of the recording medium by rotating a rotating reflector around the rotation axis thereof, wherein the rotating reflector may be a single surface mirror having a reflecting surface formed diagonally to a plane perpendicular to the rotating axis of the reflector, or a polygon mirror on which multiple reflecting surfaces are provided in a regular polygonal form centered around the rotation axis.
2. Description of the Related Art
An image forming device generally comprises an image exposure device which scans a recording medium such as a photosensitive material by a light beam emitted from a light source, and an image processing device which carries out developing processing and the like on the recording medium on which an image has been recorded by the image exposure device.
An exposure unit is provided in the image exposure device. The exposure unit comprises a light scanning apparatus, which includes plural optical members such as a lens that transforms a diffused light beam emitted from the light source into parallel rays, and a deflector, which deflects the parallel rays. There are drum type exposure units and inner spinner type exposure units. In the drum type exposure unit, a light scanning apparatus is provided at a radial direction outer side of a cylindrical drum, and a recording medium is scanned by a light beam from the exterior of the drum. In the inner spinner type exposure unit, a light scanning apparatus is provided near the center of a circular arc-shaped drum, and a recording medium is scanned by a light beam from the interior of the drum. The inner spinner type exposure unit will be focused on and described herein.
As shown in FIG. 14A, a light scanning apparatus 102 generally includes a laser 106 as a light source and a plurality of optical members mounted on a base 104. On the base 104, a collimator lens 108, a first deflecting mirror 110, a modulator 112, a second deflecting mirror 114, a beam diameter and beam shape correcting lens system 116, a prism mirror 118, and a deflector (referred to as a "spinner" hereafter) 120 are provided in that order in the direction of travel of a light beam emitted from the laser 106. The spinner 120 is rotatable, and the surface thereof facing the light beam travel direction is cut away diagonally so as to form a reflecting surface 120A.
Moreover, as shown in FIG. 14B, a circular arc-shaped drum 122, which is coaxial with the rotation center of the spinner 120, is provided in an exposure unit 100. Furthermore, a guide member 132, which guides the conveying of a recording medium 128 such as a photosensitive material along the circular arc of the drum 122, is provided. The recording medium 128 is loaded into a recording medium supplying section 124 provided underneath the light scanning apparatus 102, and is carried through between the drum 122 and the guide member 132 by rollers 130, so as to be set on the outer peripheral surface of the drum 122. Subsequently, the laser 106 emits a light beam, and the recording medium 128 is scanned by the light beam deflected by the plural optical members and by the rotation of the rotating spinner 120. The recording medium 128 scanned by the light beam is then taken-up in a recording medium take-up section 126 provided beneath the light scanning apparatus 102.
Furthermore, in an exposure unit utilizing a rotating reflector such as a polygon mirror provided with plural reflecting surfaces, the light beam is illuminated onto the rotating reflecting surfaces, and the light beam reflected by the reflecting surfaces scans the recording medium.
A D.C. motor may be used as a driving means to rotate the spinner and polygon mirror, and the supply of electrical power to the motor is stopped when the rotation of the spinner or the polygon mirror is to be stopped. Accordingly, the reflecting surfaces of the spinner or the polygon mirror will face arbitrary directions when the rotation of the spinner or the polygon mirror stops.
In the exposure unit provided with the spinner or the polygon mirror, a start of scan sensor (SOS sensor) is provided at a certain position. At the light scanning apparatus, the timing for the start of the writing of images which are to be recorded on the recording medium is set on the basis of the light beam reflected by the reflecting surface of the rotating reflector and detected by the SOS sensor.
If dust or the like adheres to the reflecting surface, the reflectance of the rotating reflector such as the spinner or the polygon mirror will be degraded. Therefore, the reflecting surface of the rotating reflector are cleaned regularly in the light scanning apparatus. Such automatic cleaning can be realized by providing, for example, a blower nozzle so that an air nozzle thereof substantially opposes the reflecting surface 120A of the spinner 120, and by causing the blower nozzle to jet out air to blow off the dust or the like adhering to the reflecting surface 120A.
However, if the reflecting surface faces an arbitrary direction instead of a certain direction when the rotating reflector stops rotating, the air jetted out from the blower nozzle may not hit the reflecting surface depending on the stopping position of the reflecting surface, so that the air may not be able to blow off the dust or the like adhering to the reflecting surface even though the blower nozzle is provided to clean the reflecting surface.
In another method of automatically cleaning the reflector surface, plural blower nozzles are provided in a ring-shaped arrangement. This method allows dust or the like adhering to the reflecting surface 120A to be blown off and the reflecting surface 120A to be cleaned regardless of what position the reflecting surface 120A of the spinner 120 faces when the spinner 120 stops. However, there has been a problem with this method in that utilization of plural nozzles complicates the overall structure of the light scanning apparatus while increasing the manufacturing cost thereof.
Thus, methods for preventing dust, dirt, or the like from being adhering easily to a reflecting surface in a light scanning apparatus have been studied.
For example, there is a spinner provided with a transparent glass cover covering the reflecting surface for preventing dust or dirt from being adhering thereto. However, such a spinner is expensive. Moreover, since the glass cover cannot completely prevent dust or dirt from being adhering to the reflecting surface, when cleaning is needed, the glass cover gets in the way of cleaning.
Moreover, in order to make it more difficult for the reflecting surface to become dirty, many methods have been contemplated such as creating a decompressed or vacuum state around the spinner or the polygon mirror, or providing a dustproofing filter. However, these methods are expensive, and cannot reliably prevent dirt from adhering to the reflecting surface.
As a means for detecting dirt on the reflecting surface, there is a method for measuring the light amount of the light beam reflected by the reflecting surface by utilizing a light amount sensor. In this case, since it is difficult to have the rotating reflector to stop in a position facing a certain direction, the light amount measurement must be carried out by synchronizing the timing when the light beam reflected by the rotating reflecting surface is illuminated onto the light amount sensor with a detected result by the SOS sensor.
Since the light beam is passed at a high speed over the light amount sensor in such light amount measuring methods, a light amount sensor or an amplifier capable of high-speed responding is required in order to improve the detecting accuracy. However, since such a sensor or amplifier capable of high-speed responding is expensive, the manufacturing cost of the light scanning apparatus increases. Moreover, there is another problem in that the detecting accuracy might deteriorate since the light amount of the light beam is detected while the spinner 120 is rotating.
Furthermore, there is yet another problem in that light amount adjustment and focus adjustment of the light beam at the time of installing the light scanning apparatus in the exposure unit is difficult since the light beam reflected by the reflecting surface 120A of the spinner 120 may not reliably be illuminated onto the sensor depending on the position or direction of the reflecting surface 120A when the spinner 120 has stopped.